Particulate enzyme preparations obtained from the cell membrane of Micrococcus luteus utilize uridine diphosphate acetyglucosamine, UDP-acetylmannosaminuronic acid and UDP-glucose for the in vitro biosynthesis of a polymer similar to the cell wall polysaccharide of this organism. Several intermediates have been observed to participate in the assembly of the polysaccharide. Present research effort is concerned with the identification of these intermediates and the determination of the overall mechanism of synthesis. Since part of the biosynthetic process can occur in a detergent solubilized system, attempts will be made to resolve the two or more enzymes suspected to be present.